(a) Field of the Invention
The invention relates to a power mesh managing method and related integrated circuit, particularly to a method for managing power mesh of a standard cell and related integrated circuit.
(b) Description of the Related Art
As the APR (automatic placement and routing) tool not only helps a circuit designer placing circuit elements at the suitable locations in the chip easily but also helps the circuit designer managing the power routing, the APR tool has become one of the indispensable tools for the circuit designer.
Generally, the APR tool uses two types of blocks to manage circuit elements. One of them is the standard cell. As the name implies, the standard cell is a type of standardized block having specific size and built-in power managing method for managing some often-used standard circuit elements, such as: flip-flops, logic gates, and the like. Then, the APR tool can neatly arrange a plurality of standard cells in the area of a chip. The other one is the macro block. The macro block is different from the standard cell. The macro block does not have fixed size and is used to manage the circuits having specific functions designed by the circuit designer, such as: SRAM, ADC, and so on.
However, the APR tool follows specific routing rules to appropriately arrange the macro block and the standard cell at the suitable locations of the chip and to draw the power network. But, as the APR tool can only perform regular management, the details of the management still needs manual adjustments by the designer. Therefore, the APR tool still needs to be improved.
Now please refer to FIG. 1 which shows a three-dimensional schematic diagram illustrating the standard cell 100 and the standard cell power supplying meshes 110, 120 managed by the APR tool according to the prior art. In general, as shown in FIG. 1, the standard cell power supplying meshes 110, 120 growing along the horizontal direction are placed along each side of the standard cell 100 according to the managing rule of the traditional APR tool. The power supplying mesh 110 conducts the external power VDD to the standard cell 100 while the power supplying mesh 120 conducts the ground power VSS to the standard cell 100.
Then, please refer to FIG. 2 which shows a three-dimensional schematic diagram illustrating the standard cell 100, the standard-cell power supplying meshes 110, 120, shown in FIG. 1, and the power supplying network 200 located above the standard cell 100. Please note that, for clarity, only three rows of standard cell 100 are shown in FIG. 2. But, in practical applications, there can be many more standard cells 100 in the chip. As shown in FIG. 2, the lower part is the standard cell and the standard cell power supplying meshes 110, 120 in FIG. 1 while the upper part is the power supplying network 200 managed by the APR tool according to the prior art. As shown in FIG. 2, the power supplying network 200 includes the horizontal power supplying mesh 210 and the vertical power supplying mesh 220. The vertical power supplying mesh 220 and the horizontal power supplying mesh 210 are located in different metal layers. The vertical power supplying mesh 220 is positioned on the layer above the horizontal power supplying mesh 210. The horizontal power supplying mesh 210 is perpendicular to the vertical power supplying mesh 220 to form a matrix. Besides, the horizontal power supplying mesh 210 includes a plurality of mutually interlaced power lines 211 and ground lines 212. The vertical power supplying mesh 220 also includes a plurality of mutually interlaced power lines 221 and ground lines 222.
Besides, the power lines 211, 221 must couple to the external power (not shown in the figure). The power lines 211, 221 couple to the above mentioned standard-cell power supplying mesh 110 through the via hole (“via”) and the via plug 230 for conducting the voltage VDD that is provided by the external power into the standard cell 100. On the other hand, the ground lines 212, 222 also must couple to the ground voltage VSS. And, the ground lines 212, 222 couple to the standard-cell power supplying mesh 120 through the via and the via plug 230 for conducting the ground voltage into the standard cell 100. Please note that, for clarity, the via 230 between the horizontal power supplying mesh 210 and the standard cell power supplying meshes 110, 120 is not shown in FIG. 2. In general, the interlacing power lines, that are at the equal potential, of the horizontal power supplying mesh 210 and the vertical power supplying mesh 220 (such as: between 211 and 221 and between 221 and 222) couple to each other at the overlapping area through the via and the via plug. The via and the via plug to couple the power supplying meshes at the overlapping area are also not shown in FIG. 2, for clarity.
Please also note that, in order to conduct the external power VDD/ground voltage VSS into the standard cell 100, the resistance between the external power and the standard cell 100 is generally properly designed to obtain better overall circuit performance. The resistance between the external power and the standard cell 100 is directly related to the number of the vias and the via plugs. As is well known to the industry, due to the resistance shunting effect, the more is the number of the vias/via plugs the more is the reduction of the resistance between the external power and the standard cell 100. Hence, the positions that can be allocated to the vias/via plugs become crucial. As mentioned before, the adjustable range of the resistance becomes larger as there are more allocable positions for the vias/via plugs. Therefore, in general, the routing rules of the APR tool are usually designed to place the vias and the via plugs, at the overlapping areas between the power supplying meshes 210/220 and the standard cell power meshes 110/120 and at the overlapping areas between the power supplying mesh 210 and the power supplying mesh 220 for coupling. However, such a design will cause some problems.
Now, please refer to FIG. 3 which shows a schematic diagram illustrating the side view of the standard cell power meshes 110, 120 and the standard-cell power supplying network 200 located in the upper layer. As shown in FIG. 3, since the horizontal power supplying mesh 210 is located in the layer below the vertical power supplying mesh 220, the horizontal power supplying mesh 210 can be coupled to the standard-cell power supplying meshes 110/120 by way of the via/via plug 230 without obstruction. Therefore, the above mentioned routing mechanism will not face too many problems. But, for the vertical power supplying mesh 220, since the vertical power supplying mesh 220 may be blocked by the horizontal power supplying mesh 210 that may be positioned between the power supplying mesh 220 located in the upper layer and the standard-cell power supplying meshes 110, 120, the power supplying mesh 220 located in the upper layer may not be able to couple to the standard-cell power supplying meshes 110, 120 below by way of the vias/via plugs. Therefore, the positions for placing the vias/via plugs become limited. As shown in FIG. 3, the via/via plug 230 that is marked by “X” indicates that the via/via plug cannot be placed at that location. That is, the via/via plug 230, that is supposed to couple the vertical power lines 221/222 in the upper layer to the standard cell power meshes 110/120 in the lower layer, is blocked by the horizontal power supplying mesh 210 and cannot be provided.
Besides, the above mentioned structure has another problem. In addition to the drawback that the horizontal power supplying mesh 210 blocks the connecting route between the vertical power supplying mesh 220 and the power supplying meshes 110/120 below. The position and the width for the horizontal power supplying mesh 210 suffer a lot of limitations to complete the above mentioned coupling mechanism. For example, if the horizontal power supplying mesh 210 is too wide and is not positioned suitably, the standard-cell power supplying meshes 110, 120 of different electrical properties can be shadowed simultaneously. Then, the standard-cell power supplying meshes 110, 120 cannot directly acquire the voltage VDD and the ground voltage VSS simultaneously through the horizontal power supplying mesh 210 or the vertical power supplying mesh 220 above. As above mentioned, the position and the width for the horizontal power supplying mesh 210 must be properly designed to avoid the above mentioned problems. However, such an approach reduces the flexibility of the routing and the routing design becomes much more complicated.
Therefore, those who are skilled in the art must develop new routing rules and layout methods to solve the above mentioned problems.